Abstract:

Objective To evaluate the patterns of sleep duration by integrating nocturnal and daytime sleep, and to explore their associations with activities of daily living (ADL) in middle-aged and older adults.

Methods The data of sleep and ADL were obtained from 11 085 subjects aged 45 and older, which were collected from the China Health and Retirement Longitudinal Study (CHARLS). At enrollment in 2011, data on nocturnal and daytime sleep duration were collected through questionnaires. Firstly, subjects were divided into three groups based on the 33rd and 66th percentiles of nocturnal sleep duration, assigned scores of 1, 2 and 3, respectively. Subsequently, subjects were divided into three groups based on the 33rd and 66th percentiles of daytime sleep duration, assigned scores of 3, 2 and 1, respectively. Finally, the scores for nocturnal and daytime sleep were summed to create a total sleep score ranging from 2 to 6. A total sleep score of 6 was defined as sleep duration pattern 1, indicating a longer nocturnal sleep duration with no or shorter daytime sleep duration. Similarly, total sleep scores of 5, 4, 3 and 2 were defined as sleep duration patterns 2, 3, 4 and 5, respectively, with sleep duration pattern 5 indicating a shorter nocturnal sleep duration and a longer daytime sleep duration. The status of ADL was assessed using the Activities of Daily Living Scale (Katz edition) at baseline and during follow-up in 2013, 2015 and 2018. The association between sleep duration patterns and the risk of ADL disability was evaluated using a Cox proportional hazards model.

Results A total of 63 015 person-years were followed, with 11 085 subjects, during which 3 239 individuals experienced ADL disability. The 33rd and 66th percentiles of the nocturnal sleep duration in the study population were 6.00 hours and 7.00 hours, respectively; while the 33rd and 66th percentiles of the daytime sleep duration were 0.00 hours and 1.00 hours, respectively. Of those, 1 522 were classified into sleep duration pattern 1, 2 196 into sleep duration pattern 2, 4 299 into sleep duration pattern 3, 2 304 into sleep duration pattern 4, and 764 into sleep duration pattern 5. Compared to sleep duration pattern 1, the risk of ADL disability of patterns 3, 4 and 5 were higher (P < 0.05), with P-value for the trend less than 0.001, after adjusting for age, sex, body mass index, marital status, educational level, residence, smoking, drinking, history of chronic diseases, depression status and season. No interaction effect between gender, age and season, and sleep duration patterns was observed (P > 0.05). Compared to subjects with nocturnal sleep duration ≥ 9 hours and daytime sleep duration < 2 hours, those with nocturnal sleep duration < 7 hours and daytime sleep duration ≥ 2 hours had a higher risk of ADL disability (P < 0.05).

Conclusion Older adults who sleep less at night but take longer naps during the day are at a higher risk of experiencing limitations in their ADL. Sleep patterns may influence ADL among middle-aged and older populations, and managing their sleep duration patterns could help prevent the onset of ADL limitations.

Key words: middle-aged and older, disability, sleep patterns, activities of daily living, China Health and Retirement Longitudinal Study